1. Field of the Invention
The present invention relates to a solid-state imaging device, a method of driving a solid-state imaging device, and an imaging apparatus.
2. Description of the Related Art
Usually, in order to operate a CMOS image sensor, a high voltage which exceeds the power supply voltage of the sensor is required. As a power supply which generates such a high voltage, a charge pump type boost circuit which can be miniaturized in a relatively easy manner, and which can be easily formed as an IC to incorporate such a sensor is often used.
In the case of the charge pump type, however, an image quality problem is principally caused by noises due to a pumping operation in which boosting is performed by an input of a clock signal. Noises which are synchronized with a pumping clock frequency of about several hundreds of kHz (200 kHz to 1 MHz) are generated.
In a CMOS sensor which is disclosed in JP-2006-19971 below, during a process of correlation double sampling, the pumping operation of a charge pump is inhibited, whereby the output from a source of generating a pumping clock signal is nulled. In this case, the pumping operation is temporarily stopped, and hence the image quality is affected by lowering of the power supply voltage of the sensor.
JP-2001-218119 below discloses a technique of, in a CCD imaging device, avoiding noises due to a phenomenon in which a boost clock signal enters an imaging signal. In the disclosed patent, using a period when the output of the imaging signal from a CCD image sensor is stopped (i.e., the horizontal blanking period or the like), the timing of a timing generating portion is set so as to apply a boost clock signal from a timing generating circuit to a controlling portion (i.e., so as to perform the pumping operation). In the case where the technique disclosed in JP-2001-218119 is applied to a solid-state imaging device such as a CMOS image sensor, however, the charge pump operation is performed in the blanking period which is a period of the CDS (correlation double sampling) operation that is most important in the pixel reading operation, with the result that the image quality is affected.
In a method of suppressing power supply noises, a low-pass filter (LPF) can be used. A low-pass filter includes a capacitor (C) and a resistor (R). When the capacitance of the capacitor is increased, the size becomes large, and a large area is occupied. In the case of external provision, the number of components to be mounted is increased, thereby impeding the miniaturization of an optical device. When the resistance R is made higher, a large voltage drop due to a current consumed by a sensor occurs. When CR is made small to raise the cutoff frequency of the LPF, the frequency is higher than the operating frequency of the charge pump system, and noises cannot be blocked.
Today, a configuration of a solid-state imaging device of the photoelectric converting layer stacking type in which a photoelectric converting layer containing an organic material that produces charges in accordance with incident light is disposed above a semiconductor substrate is proposed as a novel imaging system. The configuration is excellent in that, when the photoelectric converting layer having a high photoelectric conversion efficiency is placed on a reading circuit of a CMOS structure or the like, the imaging device can be thinned, and the aperture ratio and the sensitivity can be made high. Furthermore, the power consumption is low (the consumption current: several tens of μA), and therefore the configuration is excellent also in the feature that it is suitable for a small camera in a portable module and the like.
In a solid-state imaging device of the photoelectric converting layer stacking type, similarly with a conventional solid-state imaging device, a high voltage (about 3.3 V to 40 V) which exceeds the power supply voltage (usually, about 3.3 V) of a sensor is usually required in order to ensure a high image quality. The use of a boost circuit as a power supply for generating a high voltage has been studied so that such a high voltage is supplied. However, the image quality is inevitably reduced by power supply noises due to the operation of the boost circuit. When a low-pass filter is simply introduced in order to suppress power supply noises, however, the size of an IC chip including a solid-state imaging device of the photoelectric converting layer stacking type is increased. Therefore, the novel configuration has room for improvement.